This invention relates to data multiplexing an original video signal and an original audio signal into a cell multiplexed video and audio signal, such as a sequence of asynchronous transfer mode (ATM) cells, and to data demultiplexing the cell multiplexed video and audio signal into the original video signal and the original audio signal. Such data multiplexing and data demultiplexing are used typically in a communication network of an asynchronous transfer mode multimedia system. More particularly, this invention relates to a data multiplexing method, to a data multiplexer device, and to a data demultiplexer device.
It is already known to deal with data multiplexing and data demultiplexing of the type described. As will later be described in greater detail, a conventional data multiplexer device comprises a video processor unit for processing an original video signal into a succession of video cells having a predetermined common cell length. An audio processor unit processes an original audio signal into a like succession of audio cells having the common cell length. With additional information used as a header and/or trailer in each of the video and the audio cells, a multiplexer unit multiplexes the video and the audio cells into a cell multiplexed video and audio signal.
It should be noted in connection with the conventional data multiplexer device that the video cells correspond in number to an amount of video information carried by the original video signal. This number has consequently been determined to cover a maximum amount of the video information by inserting dummy cells in the succession of video cells and by multiplexing the video and the audio cells into the cell multiplexed video and audio signal together with the dummy cells. As a result, the cell multiplexed video and audio signal unavoidably has a deteriorated transmission efficiency.
On processed into the video cells, the original video signal is first encoded into an encoded video signal for storage in a buffer memory as a buffered datum. From the buffer memory, the buffered datum is read out as video data of a common data length which is equal to the common cell length. Inasmuch as the buffer memory is used, the video data are produced with a delay relative to the encoded video signal.
On demultiplexing the cell multiplexed video and audio signal by a data demultiplexer device into reproductions of the original video signal and the original audio signal, it is necessary to keep the delay constant. It has, however, been impossible for the conventional data multiplexer device to produce the cell multiplexed video and audio signal together with information indicative of the delay. As a consequence, it has been impossible to keep between the original video and audio signals in the reproductions the lip synchronism as called in the art.